An example of a contact bush and a plug-in connector according to the prior art is described in applicant's U.S. Pat. No. 4,834,681. This known contact bush comprises a front box section which is inserted into a chamber of a plug-in connector body and held therein, and a rear connection section to which an electric lead can be attached, for example by crimping. A window-shaped cut-out in the rigid box section constitutes a first latching element. A flexible tongue with a lug which forms a complementary second latching element is constructed in one piece with an insulator body of the plug-in connector. Both can make a latching connection by means of which the contact element is non-displaceably held in the body. If a cable is to be provided with plugs using such a contact element, the ends of the individual conductors of the cable are first fitted with contact elements and these are then inserted into the insulator body from the cable outlet side and latched there.
Such a procedure is practical and efficient if the number of conductors to be fitted per cable is low and if the risk of a contact element being inadvertently inserted into the wrong chamber of the body can be kept low by color coding of the conductors or the like.
However, in particular in the automobile industry the complexity of cabling has recently increased considerably. It is therefore necessary to a greater extent to fit plug-in connectors to cables with a large number of conductors or to cable harnesses with a complex branching pattern. When this is being done, only a single error is often sufficient to make the entire cable or cable harness unusable, since, even if the error can be localized, it is often impossible to eliminate it. After the contact element has been plugged into the insulator body, the latching elements are no longer accessible and can no longer be separated from one another, so that it is virtually impossible to release the incorrectly inserted contact elements from the insulator body. If this is in fact achieved, it is only at the price of damaging or destroying the latching elements. In this context, the lug and the tongue are particularly at risk since they are composed, like the insulator body, of plastic and are therefore substantially softer than the metal of the bush.
In particular, if the length of the cables is subjected to only small tolerances, it is often also impossible to simply cut off an incorrectly fitted plug-in connector and put a new one in its place.
If it is assumed that in a cable harness with, for example, 100 connections the probability of incorrectly fitting a single one of these connections is only 1 per thousand, this means that 10% of all completed cable harnesses are faulty. If it is also considered that in the case of multi-conductor connections the effectiveness of the prevention of errors by color coding the conductors, or in some other way, is smaller as their number becomes larger, it becomes obvious that there is a considerable requirement for contact elements or plug-in connectors which permit errors to be easily corrected even after fitting.